Noncarbon papers are roughly divided into the so-called transfer type in which the color coupler microcapsule and developer are separately coated on different papers and the self-contained type in which they are applied in two layers on paper surface or coated as a mixture. Since such coating methods, in which water or solvent-based liquids are coated on paper, are likely not only to be problematic with regard to working environment but also is accompanied by the risk of fire or explosion and, furthermore, a drying process is required to make the whole process to be complicated and a lot of energy to be required. A method for solving this problem is proposed, for example, in Examined Publication No. 7917/82. The method is for coating paper with a solid meltable coating composition by the roller or knife coating method or by gravure printing method, but the coating work is not necessarily easy, and has a demerit of requiring a large amount of developer.
The heat sensitive paper being used in large quantities for facsimile etc. has coated thereon a leuco dye and a developer and has a drawback of "base color" tinting or recording image being discolored or fading through contact of "color coupler" layer with chemicals, being thus low in chemical resistance. When it is used for, especially, POS label, importance is attached to anti-plasticizer resistance and proposed is use of over-coating method or the like for prevention of migration of plasticizer. Now heat transfer type recording paper, in which a transfer sheet coated with a layer of leuco dye and a "receiving" sheet coated with a layer of developer are used, is being developed but like the above-described non-carbon paper, this is prepared by coating paper with a liquid such as water or a solvent, hence has problems like non-carbon paper.
The present inventors, therefore, proposed earlier a developer sheet formed by integrating a sheet-like formation composed of an olefin resin and a developer and a substrate (Non-examined publication No. 148094/86).
The above-mentioned defect was eliminated by development of the aforesaid developer sheet and the performance of separate-type pressure sensitive lower paper (resistance to water, oil) was improved markedly, but there was something to be desired about light fastness and fading with time after development.
With regard to the above-mentioned situation and as a result of their intensive studies, the present inventors arrived at the invention through recognition of marked effect of dye-absorbing inorganic substance on the developing performance such as light fastness and fading with time after development.